Polyacrylonitrile carbon fiber and preparation method thereof

Abstract

The invention discloses a polyacrylonitrile carbon fiber and a preparation method thereof, and the method comprises the following steps: (1) copolymerizing acrylonitrile and acrylamidine to obtain a polymer spinning solution; (2) sequentially carrying out spinning, solidification forming, first-stage drafting, washing, oiling, drying, second-stage drafting and heat setting on the polymer spinning solution to obtain a polyacrylonitrile precursor; and (3) sequentially carrying out pre-oxidation and carbonization treatment on the polyacrylonitrile precursor to obtain the polyacrylonitrile carbon fiber. Therefore, by adopting the method, the radial structure difference of the nascent fiber can be effectively controlled, the radial structure of the obtained nascent fiber is more homogeneous, and the radially homogeneous polyacrylonitrile precursor is obtained, so that the prepared carbon fiber is more excellent in performance or larger in diameter, and meanwhile, an ammonification process link is omitted.

Description

Technical Field

[0001] The present invention belongs to the field of fibers, and particularly relates to a polyacrylonitrile carbon fiber and a preparation method thereof. Background Art

[0002] Polyacrylonitrile (PAN) fiber is the precursor of high-performance carbon fiber, which is prepared by spinning from an acrylonitrile copolymer solution. The spinning solution is usually a solution of a binary or ternary copolymer of polyacrylonitrile (PAN), and the copolymer usually contains more than 95% acrylonitrile monomer. The comonomers include two categories. One category is to improve the hydrophilicity of the PAN polymer and assist in the solidification and densification of the spinning dope filament, including itaconic acid, methacrylic acid, acrylic acid, etc.; the other category is a promoter that helps the PAN precursor fiber to promote the penetration of oxygen to the core of the fiber during the subsequent pre-oxidation process, generally having a relatively large side group, including methyl acrylate, methyl methacrylate, ethyl methacrylate, etc. The addition of the third monomer has a certain influence on the carbonization yield and the denseness of the carbon fiber. Currently, most high-performance PAN-based carbon fibers adopt the form of binary copolymerization, that is, acrylonitrile and itaconic acid are copolymerized.

[0003] The solidification and forming of the dope is one of the important control processes in PAN spinning. The reverse force regulation between the normal swelling during the extrusion of the spinning dope and the normal shrinkage force caused by solidification directly affects the radial structure distribution of the precursor fiber. Especially for PAN polymers with hydrophobic characteristics, the rapid phase transition in the aqueous coagulant will cause the polymer in the extrusion swelling to solidify and form, resulting in non-uniformity of the fiber radial structure. The larger the fiber diameter, the more significant the radial non-uniformity. Therefore, hindering and delaying the solidification rate from the outside to the inside of the fiber, so that the coagulant water can diffuse to the core of the filament is a research point that has been concerned in the industry.

[0004] Selecting a comonomer with better hydrophilicity can delay the solidification rate of the spinning dope stream in the coagulation bath, reduce the generation of large air bubbles from the outside to the inside in the radial direction of the nascent fiber, improve the compactness of the nascent fiber and reduce the radial difference. In the industry, itaconic acid is mainly used as the comonomer, but the addition amount of itaconic acid cannot be too much. Adding too much will affect the polymerization and also affect the compactness of the subsequent pre-oxidized fiber and carbon fiber. Therefore, its effect of alleviating the solidification rate is limited. To further improve the hydrophilicity of the polymer to alleviate the solidification rate of the polymer, people have ammoniated the itaconic acid structure, that is, introducing ammonia gas during polymerization or adding ammonia water in the coagulation bath to convert itaconic acid into ammonium salt, which can improve the homogeneity of the raw silk to a certain extent and then improve the performance of the carbon fiber. At the same time, using the method of converting itaconic acid into ammonium salt not only has problems of high power consumption and affecting the working environment, but also has bottlenecks in improving the homogeneity of the raw silk and the high performance of the carbon fiber. Because when the ammoniation degree is too high, the spinning dope stream does not solidify. At the same time, when developing thick-diameter fibers for cost reduction and efficiency improvement, the effect of itaconic acid ammoniation on the homogenization of spinning cannot meet the requirements. In other words, the ammoniation method is far from enough to alleviate the solidification rate during the process of the spinning dope stream solidifying into fibers. Summary of the Invention

[0005] The present invention aims to solve at least one of the above technical problems to some extent. For this reason, an object of the present invention is to provide a polyacrylonitrile carbon fiber and a preparation method thereof. By using this method, the radial structure difference of the nascent fiber can be effectively controlled, the radial structure of the obtained nascent fiber is more homogeneous, a polyacrylonitrile raw silk with radial homogeneity is obtained, so that the prepared carbon fiber has more excellent performance or a thicker diameter, and at the same time, the ammoniation process link is omitted.

[0006] In the first aspect of the present invention, a method for preparing polyacrylonitrile carbon fiber is provided, including:

[0007] (1) Copolymerizing acrylonitrile and acrylamidine to obtain a polymer spinning solution;

[0008] (2) Spinning, coagulating and forming, first-stage drawing, washing, oiling, drying, second-stage drawing and heat setting the polymer spinning solution in sequence to obtain polyacrylonitrile raw silk;

[0009] (3) Subjecting the polyacrylonitrile raw silk to pre-oxidation and carbonization treatments in sequence to obtain polyacrylonitrile carbon fiber.

[0010] Further, in step (1), the molar ratio of acrylonitrile to acrylamidine is (96.5 - 99.5):(0.5 - 3.5).

[0011] Further, in step (1), itaconic acid is also added during the copolymerization of acrylonitrile and acrylamidine.

[0012] Further, the molar ratio of the acrylonitrile, the acrylamidine and the itaconic acid is (96.5 - 99.5):(0.5 - 3.5):(0 - 1.5).

[0013] Further, in step (1), the polymerization temperature is 50°C - 65°C.

[0014] Further, the weight-average molecular weight of the polymer spinning solution is 85,000 - 205,000.

[0015] Further, in step (2), the spinning adopts a wet process, wherein the coagulation molding includes primary coagulation molding, secondary coagulation molding and tertiary coagulation molding.

[0016] For the primary coagulation molding, the coagulation bath temperature is 20°C - 30°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(0.2 - 0.6), the coagulation negative draft is 0% - 40%, and the coagulation time is 0.5 minute - 2 minutes.

[0017] Optionally, for the secondary coagulation molding, the coagulation bath temperature is 20°C - 50°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(0.5 - 1), and the coagulation time is 0.5 minute - 2 minutes.

[0018] Optionally, for the tertiary coagulation molding, the coagulation bath temperature is 20°C - 50°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(4 - 7), and the coagulation time is 0.5 minute - 2 minutes.

[0019] Optionally, the drafting medium for the primary drafting is steam at 100°C - 110°C, and the drafting multiple is 4 - 10 times.

[0020] Optionally, the drafting medium for the secondary drafting is steam at 120°C - 150°C, and the drafting multiple is 2 - 5 times.

[0021] Optionally, the heat setting temperature is 110°C - 180°C.

[0022] Optionally, the monofilament diameter of the polyacrylonitrile raw fiber is 10.5μm - 13μm, and the bulk density is 1.180 - 1.185 g / cm 3 .

[0023] Further, in step (2), the spinning adopts a dry-wet process, wherein the coagulation molding passes through an air layer of 5 mm - 10 mm.

[0024] Optionally, the solidification forming includes primary solidification forming, secondary solidification forming, and tertiary solidification forming.

[0025] Optionally, the solidification bath temperature of the primary solidification forming is 20°C - 30°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.2 - 0.6). The solidification drawing ratio is 1.5 - 3.5 times, and the solidification time is 0.5 minute - 2 minutes.

[0026] Optionally, the solidification bath temperature of the secondary solidification forming is 20°C - 50°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.5 - 1). The solidification time is 0.5 minute - 2 minutes.

[0027] Optionally, the solidification bath temperature of the tertiary solidification forming is 20°C - 50°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(4 - 7). The solidification time is 0.5 minute - 2 minutes.

[0028] Optionally, the drawing medium for the primary drawing is steam at 100°C - 110°C, and the drawing ratio is 4 - 10 times.

[0029] Optionally, the drawing medium for the secondary drawing is steam at 120°C - 150°C, and the drawing ratio is 2 - 5 times.

[0030] Optionally, the heat setting temperature is 110°C - 180°C.

[0031] Optionally, the monofilament diameter of the polypropylene raw filament is 10.5μm - 13μm, and the bulk density of the raw filament is 1.18 - 1.195 g / cm 3 .

[0032] Further, in step (2), the spinning adopts the dry-wet process, wherein the solidification forming passes through an air layer of 5mm - 10mm.

[0033] Optionally, the solidification forming includes primary solidification forming, secondary solidification forming, and tertiary solidification forming.

[0034] Optionally, the solidification bath temperature of the primary solidification forming is 20°C - 30°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.2 - 0.6). The solidification drawing ratio is 1.5 - 3.5 times, and the solidification time is 0.5 minute - 2 minutes.

[0035] Optionally, the solidification bath temperature of the secondary solidification forming is 20°C - 50°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.5 - 1). The solidification time is 0.5 minute - 2 minutes.

[0036] Optionally, the coagulation bath temperature for the three-stage coagulation forming is 20°C - 50°C. The coagulation bath comprises dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(4 - 7). The coagulation time is 0.5 minute - 2 minutes;

[0037] Optionally, the stretching medium for the first-stage stretching is steam at 100°C - 110°C, and the stretching ratio is 4 - 10 times;

[0038] Optionally, the stretching medium for the second-stage stretching is steam at 120°C - 150°C, and the stretching ratio is 2 - 5 times;

[0039] Optionally, the heat setting temperature is 110°C - 180°C;

[0040] Optionally, the monofilament diameter of the polypropylene raw filament is 8μm - 10.5μm, and the bulk density of the raw filament is 1.18 - 1.195 g / cm 3 。

[0041] Furthermore, in step (3), the pre-oxidation satisfies one or more of the following conditions:

[0042] The pre-oxidation includes 2 - 6 temperature zones;

[0043] The total treatment time of the pre-oxidation is 40 - 120 minutes;

[0044] The starting temperature of the pre-oxidation is 160°C - 230°C, and the final temperature is 260°C - 300°C;

[0045] During the pre-oxidation, the fiber tension is 40% - 90% of the breaking stress of the pre-oxidized fiber, preferably 50% - 80%;

[0046] The bulk density of the fiber obtained after the pre-oxidation is 1.32 g / cm 3 -1.55 g / cm 3 ;

[0047] Optionally, the carbonization includes low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization.

[0048] The low-temperature carbonization satisfies one or more of the following conditions:

[0049] High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 5 ppm;

[0050] The temperature of the low-temperature carbonization is 300°C - 800°C, and the time is 1.5 minutes - 6 minutes;

[0051] During the low-temperature carbonization, the fiber tension is 20%-70% of the fracture stress of the low-temperature carbonized fiber, preferably 40%-50%;

[0052] The medium-temperature carbonization meets one or more of the following conditions:

[0053] High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 5 ppm;

[0054] The temperature of the medium-temperature carbonization is 1000°C - 1400°C, and the time is 1.5 minutes - 6 minutes;

[0055] During the medium-temperature carbonization, the fiber tension is 20%-70% of the fracture stress of the medium-temperature carbonized fiber, preferably 40%-50%;

[0056] The high-temperature carbonization meets one or more of the following conditions:

[0057] High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 3 ppm;

[0058] The high-temperature carbonization temperature is 1400°C - 1600°C, and the time is 1 minute - 4 minutes.

[0059] Furthermore, in step (3), the pre-oxidation meets one or more of the following conditions:

[0060] The pre-oxidation includes 2 - 6 temperature zones;

[0061] The total treatment time of the pre-oxidation is 40 - 100 minutes;

[0062] The starting temperature of the pre-oxidation is 160°C - 210°C, and the final temperature is 260°C - 320°C;

[0063] During the pre-oxidation, the fiber tension is 40%-90% of the fracture stress of the pre-oxidized fiber, preferably 50%-80%;

[0064] The bulk density of the fiber obtained after the pre-oxidation is 1.32 g / cm 3 -1.55 g / cm 3 ;

[0065] Optionally, the carbonization includes low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization.

[0066] The low-temperature carbonization meets one or more of the following conditions:

[0067] High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or less than 5 ppm;

[0068] The temperature of the low-temperature carbonization is 300°C - 800°C, and the time is 1.5 minutes - 6 minutes;

[0069] During low-temperature carbonization, the fiber tension is 20%-70% of the breaking stress of the low-temperature carbonized fiber, preferably 40%-50%.

[0070] The medium-temperature carbonization satisfies one or more of the following conditions:

[0071] High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 5 ppm.

[0072] The temperature of the medium-temperature carbonization is 1000°C - 1400°C, and the time is 1.5 minutes - 6 minutes.

[0073] During medium-temperature carbonization, the fiber tension is 20%-70% of the breaking stress of the medium-temperature carbonized fiber, preferably 40%-50%.

[0074] The high-temperature carbonization satisfies one or more of the following conditions:

[0075] High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 3 ppm.

[0076] The high-temperature carbonization temperature is 1400°C - 1800°C, and the time is 1 minute - 4 minutes.

[0077] In the second aspect of the present invention, a polyacrylonitrile carbon fiber is provided, and the polyacrylonitrile carbon fiber is prepared by the above method.

[0078] Compared with the prior art, in the method of the present invention, the comonomer acrylamidine is added during the acrylonitrile polymerization process. It contains both a double bond and an amino group. The double bond can participate in the acrylonitrile copolymerization, and the amino group has stronger hydrophilicity, which can effectively improve the hydrophilicity of the polymer, relieve the solidification rate of the spinning dope filament, effectively control the radial structure difference of the nascent fiber, and make the radial structure of the obtained nascent fiber more homogeneous, obtaining a polyacrylonitrile raw yarn with a homogeneous radial structure. Therefore, the prepared carbon fiber has more excellent performance or a thicker diameter, and at the same time, the ammoniation process link is omitted. At the same time, the comonomer acrylamidine not only has a similar structure to acrylonitrile, but also the N on the side group of acrylamidine contains a proton hydrogen, which is conducive to the occurrence of the cyclization reaction during the pre-oxidation cyclization process of the PAN polymer. Therefore, the structure of the pre-oxidized fiber is more regular and dense, which is also beneficial to the improvement of the denseness and comprehensive performance of the carbon fiber.

[0079] The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. Detailed Embodiments

[0080] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope protected by the present invention.

[0081] As used herein, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present invention. The phrase may appear in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0082] The "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a particular parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present invention, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers, and the range defined in this way can include the end values a and b. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0083] If there is no special indication, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0084] In one aspect of the present invention, a method for preparing polyacrylonitrile carbon fiber is provided. According to an embodiment of the present invention, the method includes:

[0085] S1: copolymerizing acrylonitrile and acrylamidine to obtain a polymer spinning solution

[0086] According to an embodiment of the present invention, using azobisisobutyronitrile (AIBN) as an initiator and dimethyl sulfoxide (DMSO) as a solvent, acrylonitrile (AN) and acrylamidine are stirred and polymerized at a temperature of 50°C - 65°C and a stirring rate of 20 rpm - 60 rpm, preferably 30 rpm - 50 rpm. The polymerization reaction is carried out for 20 hours - 30 hours to obtain a polyacrylonitrile spinning dope with a weight-average molecular weight of 85,000 - 205,000 (solid content of 19% - 23%). After removing monomers and degassing the spinning dope, a polymer spinning solution is obtained. Among them, PAN accounts for 19 wt% - 23 wt% of the total mass of PAN and DMSO, AIBN accounts for 0.1% - 0.3% of the molar fraction of AN, and the viscosity of the spinning dope is 600 poises - 1200 poises at 45°C. Thus, by adding the comonomer acrylamidine during the polymerization of acrylonitrile, which contains both a double bond and an amino group, the double bond can participate in the copolymerization of acrylonitrile, and the amino group has stronger hydrophilicity, which can effectively improve the hydrophilicity of the polymer, alleviate the solidification rate of the spinning dope filament, effectively control the radial structure difference of the nascent fiber, and obtain a polyacrylonitrile raw fiber with a radial homogeneity.

[0087] According to an embodiment of the present invention, the molar ratio of acrylonitrile to acrylamidine is (96.5 - 99.5) : (0.5 - 3.5). Thus, by mixing acrylonitrile and acrylamidine in this ratio, the hydrophilicity of the polymer can be effectively improved, the solidification rate of the spinning dope filament can be alleviated, the radial structure difference of the nascent fiber can be effectively controlled, and a polyacrylonitrile raw fiber with a radial homogeneity can be obtained.

[0088] According to an embodiment of the present invention, during the copolymerization of acrylonitrile and acrylamidine, itaconic acid is also added, and the molar ratio of acrylonitrile to acrylamidine and itaconic acid is (96.5 - 99.5) : (0.5 - 3.5) : (0 - 1.5). Thus, by adding acrylamidine during the polymerization of acrylonitrile and itaconic acid, the generation of large air bubbles from the outside to the inside in the radial direction of the nascent fiber can be reduced, the compactness of the nascent fiber can be improved, and the radial difference can be reduced.

[0089] S2: The polymer spinning solution is successively subjected to spinning, coagulation molding, primary drawing, washing, oiling, drying, secondary drawing, and heat setting to obtain a polyacrylonitrile raw fiber.

[0090] According to an embodiment of the present invention, the spinning can adopt a wet spinning process. Among them, the solidification and forming includes primary solidification and forming, secondary solidification and forming, and tertiary solidification and forming. The solidification bath temperature of the primary solidification and forming is 20°C - 30°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.2 - 0.6). The solidification negative draft is 0% - 40%, and the solidification time is 0.5 minute - 2 minutes; the solidification bath temperature of the secondary solidification and forming is 20°C - 50°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.5 - 1), and the solidification time is 0.5 minute - 2 minutes; the solidification bath temperature of the tertiary solidification and forming is 20°C - 50°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(4 - 7), and the solidification time is 0.5 minute - 2 minutes; the stretching medium for the primary stretching is steam at 100°C - 110°C, and the stretching multiple is 4 - 10 times; the stretching medium for the secondary stretching is steam at 120°C - 150°C, and the stretching multiple is 2 - 5 times; the heat setting temperature is 110°C - 180°C. Specifically, using this wet spinning process, the single filament diameter of the obtained polyacrylonitrile precursor fiber is 10.5μm - 13μm, and the bulk density is 1.180 - 1.185g / cm 3 , and this precursor fiber can be used for the preparation of high-strength and medium-modulus carbon fibers with a thick diameter.

[0091] According to another embodiment of the present invention, the spinning adopts a dry-jet wet spinning process. Among them, the solidification and forming passes through an air layer of 5mm - 10mm; the solidification and forming includes primary solidification and forming, secondary solidification and forming, and tertiary solidification and forming. The solidification bath temperature of the primary solidification and forming is 20°C - 30°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.2 - 0.6). The solidification stretching multiple is 1.5 - 3.5 times, and the solidification time is 0.5 minute - 2 minutes; the solidification bath temperature of the secondary solidification and forming is 20°C - 50°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.5 - 1), and the solidification time is 0.5 minute - 2 minutes; the solidification bath temperature of the tertiary solidification and forming is 20°C - 50°C. The solidification bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(4 - 7), and the solidification time is 0.5 minute - 2 minutes; the stretching medium for the primary stretching is steam at 100°C - 110°C, and the stretching multiple is 4 - 10 times; the stretching medium for the secondary stretching is steam at 120°C - 150°C, and the stretching multiple is 2 - 5 times; the heat setting temperature is 110°C - 180°C. Specifically, using this dry-jet wet spinning process, the single filament diameter of the obtained polypropylene precursor fiber is 10.5μm - 13μm, and the bulk density of the precursor fiber is 1.18 - 1.195g / cm 3, the raw silk can be used for the preparation of high-strength and medium-modulus carbon fibers with a thick diameter.

[0092] According to another embodiment of the present invention, the spinning adopts another dry-wet spinning process, wherein the solidification and forming process passes through an air layer of 5 mm - 10 mm; the solidification and forming process includes primary solidification and forming, secondary solidification and forming, and tertiary solidification and forming. The temperature of the coagulation bath for the primary solidification and forming is 20°C - 30°C, the coagulation bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.2 - 0.6). The coagulation drawing ratio is 1.5 - 3.5 times, and the coagulation time is 0.5 minute - 2 minutes; the temperature of the coagulation bath for the secondary solidification and forming is 20°C - 50°C, the coagulation bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.5 - 1), and the coagulation time is 0.5 minute - 2 minutes; the temperature of the coagulation bath for the tertiary solidification and forming is 20°C - 50°C, the coagulation bath includes dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(4 - 7), and the coagulation time is 0.5 minute - 2 minutes; the drawing medium for the primary drawing is steam at 100°C - 110°C, and the drawing ratio is 4 - 10 times; the drawing medium for the secondary drawing is steam at 120°C - 150°C, and the drawing ratio is 2 - 5 times; the heat setting temperature is 110°C - 180°C. Specifically, by using this dry-wet spinning process, the single-filament diameter of the obtained polypropylene raw silk is 8 μm - 10.5 μm, and the bulk density of the raw silk is 1.18 - 1.195 g / cm 3 , the raw silk can be used for the preparation of ultra-high-strength and medium-modulus carbon fibers.

[0093] S3: Subject the polyacrylonitrile raw silk to pre-oxidation and carbonization treatments in sequence to obtain polyacrylonitrile carbon fibers.

[0094] According to an embodiment of the present invention, the pre-oxidation and carbonization treatments for the preparation of the high-strength and medium-modulus carbon fibers with a thick diameter can adopt the following conditions:

[0095] The pre-oxidation satisfies one or more of the following conditions: the pre-oxidation includes 2 - 6 temperature zones; the total treatment time of the pre-oxidation is 40 minutes - 120 minutes; the starting temperature of the pre-oxidation is 160°C - 230°C, and the final temperature is 260°C - 300°C; the fiber tension during the pre-oxidation is 40% - 90% of the breaking stress of the pre-oxidized fiber, preferably 50% - 80%; the bulk density of the fiber obtained after the pre-oxidation is 1.32 g / cm 3 -1.55 g / cm 3; The carbonization includes low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization. The low-temperature carbonization satisfies one or more of the following conditions: using high-purity nitrogen as the protective gas, with the oxygen content in the nitrogen being less than or equal to 5 ppm; the temperature of the low-temperature carbonization is 300°C - 800°C, and the time is 1.5 minutes - 6 minutes; the fiber tension during the low-temperature carbonization is 20% - 70% of the fracture stress of the low-temperature carbonized fiber, preferably 40% - 50%; the medium-temperature carbonization satisfies one or more of the following conditions: using high-purity nitrogen as the protective gas, with the oxygen content in the nitrogen being less than or equal to 5 ppm; the temperature of the medium-temperature carbonization is 1000°C - 1400°C, and the time is 1.5 minutes - 6 minutes; the fiber tension during the medium-temperature carbonization is 20% - 70% of the fracture stress of the medium-temperature carbonized fiber, preferably 40% - 50%; the high-temperature carbonization satisfies one or more of the following conditions: using high-purity nitrogen as the protective gas, with the oxygen content in the nitrogen being less than or equal to 3 ppm; the high-temperature carbonization temperature is 1400°C - 1600°C, and the time is 1 minute - 4 minutes. Specifically, the above spinning process uses the as-spun fiber obtained by the wet spinning process and is subjected to this pre-oxidation and carbonization treatment. The obtained thick-diameter high-strength medium-modulus carbon fiber with a regular groove structure on the surface has a tensile strength ≥5500 MPa, a tensile modulus of 294 ± 10 GPa, and a bulk density of 1.80 - 1.82 g / cm 3 , and the equivalent diameter is 7 ± 0.2 μm; the as-spun fiber obtained by the above dry-wet spinning process is subjected to this pre-oxidation and carbonization treatment, and the obtained thick-diameter high-strength medium-modulus carbon fiber with a smooth surface has a tensile strength ≥5880 MPa, a tensile modulus of 294 ± 10 GPa, and a bulk density of 1.80 - 1.82 g / cm 3 , and the equivalent diameter is 7 ± 0.2 μm.

[0096] According to an embodiment of the present invention, the pre-oxidation and carbonization treatment for preparing the above ultra-high-strength medium-modulus carbon fiber can adopt the following conditions:

[0097] The pre-oxidation satisfies one or more of the following conditions: the pre-oxidation includes 2 - 6 temperature zones; the total treatment time of the pre-oxidation is 40 minutes - 100 minutes; the starting temperature of the pre-oxidation is 160°C - 210°C, and the final temperature is 260°C - 320°C; the fiber tension during the pre-oxidation is 40% - 90% of the fracture stress of the pre-oxidized fiber, preferably 50% - 80%; the bulk density of the fiber obtained after the pre-oxidation is 1.32 g / cm 3 -1.55 g / cm 3; The carbonization includes low-temperature carbonization, medium-temperature carbonization and high-temperature carbonization. The low-temperature carbonization satisfies one or more of the following conditions: using high-purity nitrogen as the protective gas, with the oxygen content in the nitrogen being lower than or equal to 5 ppm; the temperature of the low-temperature carbonization is 300°C - 800°C, and the time is 1.5 minutes - 6 minutes; the fiber tension during the low-temperature carbonization is 20% - 70% of the fracture stress of the low-temperature carbonized fiber, preferably 40% - 50%; the medium-temperature carbonization satisfies one or more of the following conditions: using high-purity nitrogen as the protective gas, with the oxygen content in the nitrogen being lower than or equal to 5 ppm; the temperature of the medium-temperature carbonization is 1000°C - 1400°C, and the time is 1.5 minutes - 6 minutes; the fiber tension during the medium-temperature carbonization is 20% - 70% of the fracture stress of the medium-temperature carbonized fiber, preferably 40% - 50%; the high-temperature carbonization satisfies one or more of the following conditions: using high-purity nitrogen as the protective gas, with the oxygen content in the nitrogen being lower than or equal to 3 ppm; the high-temperature carbonization temperature is 1400°C - 1800°C, and the time is 1 minute - 4 minutes. Specifically, the above spinning uses the raw silk obtained by another dry-wet spinning process, which is subjected to this pre-oxidation and carbonization treatment to obtain ultra-high-strength and medium-modulus carbon fibers with a smooth surface, a tensile strength ≥ 8.0 GPa, a tensile modulus of 315 ± 10 GPa, and a bulk density in the range of 1.80 - 1.83 g / cm 3 , and an equivalent diameter of 5 ± 0.2 μm.

[0098] The method for preparing polyacrylonitrile carbon fibers according to the embodiments of the present invention has the following three advantages: 1. The step of ammoniation in the preparation of conventional raw silk can be omitted, and the hydrophilic effect of the polymer in the spinning dope stream is better, and the radial structure of the nascent fiber is more homogeneous, so the performance of the prepared carbon fiber is more excellent or the diameter is thicker; 2. The elemental composition of acrylamidine is the same as that of acrylonitrile, so the non-carbon elements introduced into the system are less, which is beneficial to improving the denseness of the carbon fiber, and at the same time, the carbonization yield is increased by 1% - 2%; 3. Acrylamidine is more similar in structure to acrylonitrile, and the N on the side group contains a proton hydrogen, which is conducive to the occurrence of cyclization reactions during the pre-oxidation cyclization process of the PAN polymer. Therefore, the structure of the pre-oxidized fiber is more regular and dense, which is also beneficial to the improvement of the denseness and comprehensive performance of the carbon fiber.

[0099] In the second aspect of the present invention, a polyacrylonitrile carbon fiber is proposed, and the polyacrylonitrile carbon fiber is prepared by the above method.

[0100] It should be noted that the features and advantages described above for the method for preparing polyacrylonitrile carbon fibers also apply to this polyacrylonitrile carbon fiber, and will not be elaborated here.

[0101] The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention. For those embodiments where specific technologies or conditions are not specified, the technologies or conditions described in the literature in this field or according to the product specifications are followed. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchases.

[0102] Example 1

[0103] (1) Preparation of polyacrylonitrile spinning solution

[0104] Acrylonitrile, itaconic acid, and acrylamidine were blended and put into a polymerization reaction kettle in a molar ratio of 99:0.5:0.5. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to acrylonitrile monomer was added. Azobisisobutyronitrile (AIBN) was added as an initiator, and the dosage of the initiator was 0.15 mol% of acrylonitrile monomer. Stirring polymerization was carried out at a temperature of 61 °C and a rate of 40 rpm. After 22 hours of polymerization reaction, a spinning dope with a viscosity of 800 poises at 45 °C measured by a rotational viscometer was obtained.

[0105] After degassing and defoaming, a spinning solution was prepared. The acrylonitrile copolymer content in the obtained polymer solution was 21 wt%.

[0106] (2) Wet spinning of the precursor fiber

[0107] A Coagulation and shaping of the spinning solution: Wet spinning was used, and it entered the coagulation bath for coagulation and shaping. First, it entered the first-stage coagulation bath with a coagulation bath temperature of 20 °C, a volume ratio of dimethyl sulfoxide to water in the coagulation bath of 1:0.3, a coagulation time of 1.5 minutes, and a coagulation negative draw ratio of -30%. After the coagulated filament left the first-stage coagulation bath, it entered the second-stage coagulation bath with a coagulation bath temperature of 45 °C, a volume ratio of dimethyl sulfoxide to water in the coagulation bath of 1:1, and a coagulation time of 1.5 minutes. After the coagulated filament left the second-stage coagulation bath, it entered the third-stage coagulation bath with a coagulation bath temperature of 45 °C, a volume ratio of dimethyl sulfoxide to water in the coagulation bath of 1:5.7, and a coagulation time of 1.5 minutes.

[0108] B First-stage drawing: The coagulated filament was drawn in 100 °C steam, and the draw ratio was 4.8 times.

[0109] C Washing, oiling, and drying densification of the drawn filament: After the drawn filament was washed by conventional means to remove the residual solvent, it was oiled and dried and densified by a hot roller.

[0110] D Second-stage drawing: The dried and densified filament was drawn in 140 °C superheated steam, and the draw ratio was 2.5 times.

[0111] E Heat setting: The filament after the second-stage drawing was heat-set at 150 °C. After heat setting, it was wound into a bobbin by a winding machine to obtain polyacrylonitrile carbon fiber precursor filaments.

[0112] The obtained raw silk has a single-filament equivalent diameter of 11 μm and a bulk density of 1.180 g / cm 3 , and has a groove structure on the surface.

[0113] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0114] A Pre-oxidation: Using the gradient heating method in an air atmosphere, the raw silk is subjected to pre-oxidation stabilization treatment in 6 temperature zones. The starting temperature of pre-oxidation is 210 °C, and the ending temperature of pre-oxidation is 270 °C. During pre-oxidation, the fiber tension is controlled at 50% of the breaking stress of the corresponding pre-oxidized fiber according to the degree of pre-oxidation. After pre-oxidation for 80 minutes, a pre-oxidized fiber with a bulk density of 1.39 g / cm 3 is obtained.

[0115] B Low-temperature carbonization

[0116] The obtained pre-oxidized fiber is put into a low-temperature carbonization furnace for low-temperature carbonization treatment. High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is 1 ppm. The low-temperature carbonization temperature is 580 °C. According to the requirement of fiber diameter, the fiber tension is 40% of the breaking stress of the corresponding low-temperature carbonized fiber; the low-temperature carbonization time is 3 minutes;

[0117] C Medium-temperature carbonization

[0118] After the fiber exits the low-temperature carbonization furnace, it enters a medium-carbon furnace for medium-temperature carbonization treatment. High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is 1 ppm. The high-temperature carbonization temperature is 1100 °C, and the fiber tension is 45% of the breaking stress of the corresponding medium-temperature carbonized fiber; the medium-temperature carbonization time is 3 minutes.

[0119] D High-temperature carbonization

[0120] After the fiber exits the medium-temperature carbonization furnace, it enters a high-carbon furnace for high-temperature carbonization treatment. High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is 1 ppm. The high-temperature carbonization temperature is 1500 °C. After high-temperature carbonization for 3 minutes, polyacrylonitrile carbon fiber is obtained.

[0121] The performance of the prepared carbon fiber is tested according to GB3362 "Carbon Fiber Test Standard" (the same below). The results are as follows: Cross-section: nearly circular, single-filament equivalent diameter: 7 μm, bulk density: 1.80 g / cm 3 , Tensile strength: 5630 MPa, Tensile modulus: 295 GPa, Carbonization yield: 53.5%.

[0122] Example 2

[0123] (1) Preparation of polyacrylonitrile spinning solution

[0124] Acrylonitrile and acrylamidine were blended and put into a polymerization reactor in a molar ratio of 97.5:2.5. The remaining formulation and process were the same as in Example 1. The viscosity of the spinning dope at 45 °C was measured to be 780 poises by a rotational viscometer.

[0125] After degassing and de-bubbling, a spinning solution was obtained. The acrylonitrile copolymer content in the spinning solution was 21 wt%.

[0126] (2) Wet spinning of the precursor fiber

[0127] The coagulation and shaping of the spinning solution were the same as in Example 1. The equivalent diameter of the single filament of the obtained precursor fiber was 12.5 μm, and the bulk density was 1.185 g / cm 3 , and the surface had a groove structure.

[0128] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0129] Except that the mid-temperature carbonization temperature was 1150 °C, the high-temperature carbonization temperature was 1550 °C, the pre-oxidation starting temperature was 205 °C, the termination temperature was 265 °C, and the tension was controlled at 60% of the breaking stress of the corresponding pre-oxidized fiber according to the degree of pre-oxidation, and the fiber tension was 50% of the breaking stress of the corresponding low-temperature carbonized fiber. The other steps and processes of pre-oxidation, low-temperature carbonization, mid-temperature carbonization and high-temperature carbonization were the same as in Example 1. The properties of the finally prepared carbon fiber were: equivalent diameter: 7.1 μm, bulk density: 1.805 g / cm 3 , tensile strength: 5880 MPa, tensile modulus: 298 GPa, carbonization yield: 53.8%.

[0130] Example 3

[0131] (1) Preparation of polyacrylonitrile spinning solution

[0132] Acrylonitrile, itaconic acid and acrylamidine were blended and put into a polymerization reactor in a molar ratio of 97:0.5:2.5. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the acrylonitrile monomer was added, and the initiator azobisisobutyronitrile (AIBN) was added. The dosage of the initiator was 0.12 mol% of the acrylonitrile monomer. Stirring polymerization was carried out at a temperature of 60 °C and a rate of 45 rpm. After 23 hours of polymerization reaction, a spinning dope with a rotational viscosity of 1020 poises at 45 °C was obtained.

[0133] After degassing and de-bubbling, a spinning solution was obtained. The acrylonitrile copolymer content in the spinning solution was 21.2 wt%.

[0134] (2) Dry-jet wet spinning of the precursor fiber

[0135] Coagulation and forming of the spinning solution: The dry-wet spinning method is adopted. After the fiber leaves the spinneret hole, it enters the first-stage coagulation bath after passing through a 9-mm-high air environment. The temperature of the coagulation bath is 25°C, the volume ratio of dimethyl sulfoxide to water in the coagulation bath is 1:0.33, the coagulation time is 1 minute, and the coagulation draft is 1.8 times; after the coagulated filament leaves the first-stage coagulation bath, it enters the second-stage coagulation bath. The temperature of the coagulation bath is 25°C, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath is 1:1, and the coagulation time is 1.5 minutes; after the coagulated filament leaves the second-stage coagulation bath, it enters the third-stage coagulation bath. The temperature of the coagulation bath is 25°C, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath is 1:5.7, and the coagulation time is 1.5 minutes.

[0136] (2) The draft ratios of B and D in B-E are 5 and 3.5 respectively, and the rest are the same as in Example 1. The equivalent diameter of the monofilament of the as-prepared precursor fiber is 12.0 μm, and the bulk density is 1.187 g / cm 3 。

[0137] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0138] A Pre-oxidation: The precursor fiber is subjected to pre-oxidation and stabilization treatment in 4 temperature zones in an air atmosphere by the gradient heating method. The starting temperature of pre-oxidation is 220°C, and the ending temperature of pre-oxidation is 275°C. During pre-oxidation, the fiber tension is controlled at 60% of the breaking stress of the pre-oxidized fiber according to the degree of pre-oxidation. After pre-oxidation for 60 minutes, the pre-oxidized fiber with a bulk density of 1.39 g / cm 3 is obtained. In B-D, the low-temperature carbonization temperature is 600°C, and the process conditions of the remaining low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization are the same as in Example 2.

[0139] The equivalent diameter of the carbon fiber monofilament obtained: 7.05 μm, the bulk density: 1.81 g / cm 3 , the tensile strength: 5980 MPa, the tensile modulus: 299 GPa, and the carbonization yield: 54.5%.

[0140] Example 4

[0141] (1) Preparation of polyacrylonitrile spinning solution

[0142] Acrylonitrile and acrylamidine are blended and put into a polymerization reactor in a molar ratio of 96.5:3.5. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the acrylonitrile monomer is added, and the initiator azobisisobutyronitrile (AIBN) is added. The dosage of the initiator is 0.12 mol% of the acrylonitrile monomer. Stir and polymerize at a temperature of 60°C and a rate of 45 rpm. After 23 hours of polymerization reaction, a spinning dope with a rotational viscosity of 1000 poises at 45°C is obtained.

[0143] After removing monomers and degassing, the spinning solution is obtained. The content of the acrylonitrile copolymer in the spinning solution is 21.1 wt%.

[0144] (2) Dry-jet wet spinning of the precursor fiber

[0145] A Coagulation and shaping of the spinning solution: Dry-wet spinning is adopted. After the fiber leaves the spinneret hole, it enters the first-stage coagulation bath after passing through a 7-mm-high air environment. The temperature of the coagulation bath is 25°C, the volume ratio of dimethyl sulfoxide to water in the coagulation bath is 1:0.33, the coagulation time is 1 minute, and the coagulation draft is 2.0 times. After the coagulated filament leaves the first-stage coagulation bath, it enters the second-stage coagulation bath. The temperature of the coagulation bath is 25°C, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath is 1:1. The coagulation time is 1.5 minutes. After the coagulated filament leaves the second-stage coagulation bath, it enters the third-stage coagulation bath. The temperature of the coagulation bath is 25°C, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath is 1:5.7. The coagulation time is 1.5 minutes.

[0146] (2) The draw ratios of B and D in B - E are 5 and 4 respectively, and the rest are the same as in Example 1. The equivalent diameter of the single filament of the prepared precursor fiber is 8.9 μm, and the bulk density is 1.189 g / cm 3 .

[0147] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0148] A Pre-oxidation: Using the gradient heating method in an air atmosphere, the precursor fiber is subjected to pre-oxidation and stabilization treatment in 4 temperature zones. The starting temperature of pre-oxidation is 205°C, and the ending temperature of pre-oxidation is 265°C. During pre-oxidation, the fiber tension is controlled at 60% of the fracture stress of the pre-oxidized fiber according to the degree of pre-oxidation. The pre-oxidation time is 60 minutes, and the pre-oxidized fiber with a bulk density of 1.39 g / cm 3 is obtained;

[0149] (3) In B - D of (3), the high-temperature carbonization temperature is 1700°C, and the process conditions of the remaining low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization are the same as in Example 2.

[0150] The equivalent diameter of the single filament of the obtained carbon fiber: 5.1 μm, bulk density: 1.82 g / cm 3 , tensile strength: 8050 MPa, tensile modulus: 318 GPa, carbonization yield: 53.0%.

[0151] Comparative Example 1

[0152] (1) Preparation of polyacrylonitrile spinning solution

[0153] Acrylonitrile, itaconic acid, and methyl acrylate were blended in a molar ratio of 99:0.5:0.5 and put into a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the acrylonitrile monomer was added, and the initiator azobisisobutyronitrile (AIBN) was added. The dosage of the initiator was 0.15 mol% of the acrylonitrile monomer. Stirring polymerization was carried out at a temperature of 61°C and a rate of 40 rpm. After 22 hours of polymerization reaction, a spinning dope with a viscosity of 790 poises at 45°C measured by a rotational viscometer was obtained.

[0154] After degassing and de-bubbling, a spinning solution was prepared, and the acrylonitrile copolymer content in the obtained polymer solution was 21 wt%.

[0155] (2) Wet spinning of the precursor fiber

[0156] For the coagulation and forming process of Spinning Solution A, except that ammonia water was added to the coagulation bath to adjust the pH value of the coagulation bath to 8.5, the other processes and conditions were the same as those in Example 1.

[0157] B - E in (2) were the same as those in Example 1

[0158] The equivalent diameter of the single filament of the obtained precursor fiber was 11.5 μm, and the bulk density was 1.175 g / cm 3 , and the surface had a groove structure.

[0159] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0160] The pre-oxidation process conditions of Spinning Solution A were the same as those in Example 1, and pre-oxidized fibers with a bulk density of 1.368 g / cm were obtained; 3

[0161] The process conditions of B - D in (3) were the same as those in Example 1

[0162] The equivalent diameter of the single filament of the obtained carbon fiber: 7 μm, bulk density: 1.77 g / cm 3 , tensile strength: 5170 MPa, tensile modulus: 282 GPa, carbonization yield: 52.2%.

[0163] Comparative Example 2

[0164] (1) Preparation of polyacrylonitrile spinning dope

[0165] Acrylonitrile and itaconic acid were blended in a molar ratio of 97:3 and put into a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the acrylonitrile monomer was added, and the initiator azobisisobutyronitrile (AIBN) was added. The dosage of the initiator was 0.12 mol% of the acrylonitrile monomer. Stirring polymerization was carried out at a temperature of 60°C and a rate of 45 rpm. After 23 hours of polymerization reaction, a spinning dope with a rotational viscosity of 1030 poises at 45°C was obtained.

[0166] After degassing and defoaming, a spinning solution is prepared, and the acrylonitrile copolymer content in the spinning solution is 21 wt%.

[0167] (2) Dry-jet wet spinning of the precursor fiber

[0168] In the solidification and forming process of spinning solution A, except adding ammonia water to adjust the pH value of the coagulation bath to 8.5 in the coagulation bath, the other processes and conditions are the same as those in Example 3.

[0169] B-E in (2) are the same as those in Example 3

[0170] The equivalent diameter of the single filament of the obtained precursor fiber is 11.9 μm, and the bulk density is 1.177 g / cm 3 .

[0171] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0172] The pre-oxidation process conditions in A are the same as those in Example 3, and pre-oxidized fibers with a bulk density of 1.370 g / cm 3 are obtained;

[0173] The process conditions of B-D in (3) are the same as those in Example 3

[0174] The equivalent diameter of the single filament of the obtained carbon fiber: 6.95 μm, bulk density: 1.78 g / cm 3 , tensile strength: 5280 MPa, tensile modulus: 283 GPa. The carbonization yield is 52.5%.

[0175] Comparative Example 3

[0176] (1) Preparation of polyacrylonitrile spinning solution

[0177] Acrylonitrile and itaconic acid are blended and put into a polymerization reactor in a molar ratio of 96.5:3.5, and then dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the acrylonitrile monomer is added. Azobisisobutyronitrile (AIBN) is added as an initiator, and the dosage of the initiator is 0.12 mol% of the acrylonitrile monomer. Stirring polymerization is carried out at a temperature of 60 °C and a rate of 45 rpm. After 23 hours of polymerization reaction, a spinning dope with a rotational viscosity of 1100 poises at 45 °C is obtained.

[0178] After degassing and defoaming, a spinning solution is prepared, and the acrylonitrile copolymer content in the spinning solution is 21.2 wt%.

[0179] (2) Dry-jet wet spinning of the precursor fiber

[0180] In the solidification and forming process of spinning solution A, except adding ammonia water to adjust the pH value of the coagulation bath to 8.5 in the coagulation bath, the other processes and conditions are the same as those in Example 4.

[0181] B-E in (2) are the same as those in Example 4

[0182] The obtained raw silk has a single-filament equivalent diameter of 12.0 μm and a bulk density of 1.178 g / cm 3 .

[0183] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0184] A The pre-oxidation process conditions are the same as those in Example 4, and pre-oxidized fibers with a bulk density of 1.375 g / cm 3 are obtained.

[0185] (3) The process conditions of B - D are the same as those in Example 4

[0186] The single-filament equivalent diameter of the obtained carbon fiber: 5.1 μm, bulk density: 1.785 g / cm 3 , tensile strength: 6360 MPa, tensile modulus: 298 GPa. The carbonization yield is 51.5%.

[0187] The bulk densities of the raw silk in Examples 1 - 4, as well as the equivalent diameters, bulk densities, tensile strengths, tensile moduli and carbon yields of the carbon fibers, are shown in Table 1.

[0188] Table 1

[0189]

[0190]

[0191] Conclusion: Comparing Example 1 with Comparative Example 1, the equivalent diameter of the carbon fiber in Example 1 is the same as that in Comparative Example 1, but the bulk density, tensile strength, tensile modulus and carbonization yield of the carbon fiber in Example 1 are all higher than those in Comparative Example 1; comparing Example 3 with Comparative Example 2, the equivalent diameter, bulk density, tensile strength, tensile modulus and carbonization yield of the carbon fiber in Example 3 are all higher than those in Comparative Example 2; comparing Example 4 with Comparative Example 3, the equivalent diameter of the carbon fiber in Example 4 is the same as that in Comparative Example 3, but the bulk density, tensile strength, tensile modulus and carbonization yield of the carbon fiber are all higher than those in Comparative Example 3; it shows that adding acrylamidine monomer during the acrylonitrile polymerization process can obtain radially homogeneous polyacrylonitrile raw silk, which is thus beneficial to improving the denseness, mechanical properties and carbonization yield of the carbon fiber.

[0192] As described above, the above are only specific embodiments of the invention covered by the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing polyacrylonitrile carbon fiber, characterized in that, Comprising: (1) Copolymerizing acrylonitrile and acrylamidine to obtain a polymer spinning solution; (2) Subjecting the polymer spinning solution to spinning, coagulation molding, primary drawing, washing, oiling, drying, secondary drawing and heat setting in sequence to obtain polyacrylonitrile precursor filaments; (3) Subjecting the polyacrylonitrile precursor filaments to pre-oxidation and carbonization treatments in sequence to obtain polyacrylonitrile carbon fibers.

2. The method according to claim 1, wherein In step (1), the molar ratio of the acrylonitrile to the acrylamidine is (96.5 - 99.5):(0.5 - 3.5).

3. The method according to claim 1 or 2, characterized in that In step (1), itaconic acid is further added during the copolymerization of the acrylonitrile and the acrylamidine; Optionally, the molar ratio of the acrylonitrile to the acrylamidine and the itaconic acid is (96.5 - 99.5):(0.5 - 3.5):(0 - 1.5).

4. The method according to claim 1, wherein In step (1), the polymerization temperature is 50°C - 65°C; Optionally, the weight-average molecular weight of the polymer spinning solution is 85,000 - 205,000.

5. The method according to claim 1, wherein In step (2), the spinning adopts a wet process, wherein the coagulation molding includes primary coagulation molding, secondary coagulation molding and tertiary coagulation molding, The coagulation bath temperature for the primary coagulation molding is 20°C - 30°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(0.2 - 0.6), the coagulation negative drawing is 0% to -40%, and the coagulation time is 0.5 minute - 2 minutes; Optionally, the coagulation bath temperature for the secondary coagulation molding is 20°C - 50°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(0.5 - 1), and the coagulation time is 0.5 minute - 2 minutes; Optionally, the coagulation bath temperature for the tertiary coagulation molding is 20°C - 50°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(4 - 7), and the coagulation time is 0.5 minute - 2 minutes; Optionally, the drawing medium for the primary drawing is steam at 100°C - 110°C, and the drawing ratio is 4 - 10 times; Optionally, the drawing medium for the secondary drawing is steam at 120°C - 150°C, and the drawing ratio is 2 - 5 times; Optionally, the heat setting temperature is 110°C - 180°C; Optionally, the monofilament diameter of the polyacrylonitrile precursor fiber is 10.5 μm - 13 μm, and the bulk density is 1.180 - 1.185 g / cm 3 .

6. The method according to claim 1, wherein In step (2), the spinning adopts a dry-wet process, wherein the coagulation molding passes through an air layer of 5 mm - 10 mm; Optionally, the coagulation molding includes primary coagulation molding, secondary coagulation molding and tertiary coagulation molding, Optionally, the coagulation bath temperature for the primary coagulation molding is 20°C - 30°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(0.2 - 0.6), the coagulation drawing ratio is 1.5 - 3.5 times, and the coagulation time is 0.5 minute - 2 minutes; Optionally, the coagulation bath temperature for the secondary coagulation molding is 20°C - 50°C, the coagulation bath comprises dimethyl sulfoxide and water, the volume ratio of the dimethyl sulfoxide to the water is 1:(0.5 - 1), and the coagulation time is 0.5 minute - 2 minutes; Optionally, the coagulation bath temperature for the three-stage coagulation forming is 20°C - 50°C. The coagulation bath comprises dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(4 - 7). The coagulation time is 0.5 minute - 2 minutes; Optionally, the stretching medium for the first-stage stretching is steam at 100°C - 110°C, and the stretching ratio is 4 - 10 times; Optionally, the stretching medium for the second-stage stretching is steam at 120°C - 150°C, and the stretching ratio is 2 - 5 times; Optionally, the heat setting temperature is 110°C - 180°C; Optionally, the monofilament diameter of the polypropylene tow is 10.5 μm - 13 μm, and the bulk density of the tow is 1.18 - 1.195 g / cm 3 .

7. The method according to claim 1, characterized in that, In step (2), the spinning adopts the dry-wet process, wherein the coagulation forming passes through an air layer of 5 mm - 10 mm; Optionally, the coagulation forming includes first-stage coagulation forming, second-stage coagulation forming, and third-stage coagulation forming; Optionally, the coagulation bath temperature for the first-stage coagulation forming is 20°C - 30°C. The coagulation bath comprises dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.2 - 0.6). The coagulation stretching ratio is 1.5 - 3.5 times, and the coagulation time is 0.5 minute - 2 minutes; Optionally, the coagulation bath temperature for the second-stage coagulation forming is 20°C - 50°C. The coagulation bath comprises dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(0.5 - 1). The coagulation time is 0.5 minute - 2 minutes; Optionally, the coagulation bath temperature for the third-stage coagulation forming is 20°C - 50°C. The coagulation bath comprises dimethyl sulfoxide and water, and the volume ratio of dimethyl sulfoxide to water is 1:(4 - 7). The coagulation time is 0.5 minute - 2 minutes; Optionally, the stretching medium for the first-stage stretching is steam at 100°C - 110°C, and the stretching ratio is 4 - 10 times; Optionally, the stretching medium for the second-stage stretching is steam at 120°C - 150°C, and the stretching ratio is 2 - 5 times; Optionally, the heat setting temperature is 110°C - 180°C; Optionally, the monofilament diameter of the polypropylene tow is 8 μm - 10.5 μm, and the bulk density of the tow is 1.18 - 1.195 g / cm 3 .

8. The method according to any one of claims 5-7, characterized in that, In step (3), the pre-oxidation satisfies one or more of the following conditions: The pre-oxidation includes 2 - 6 temperature zones; The total treatment time of the pre-oxidation is 40 minutes - 120 minutes; The starting temperature of the pre-oxidation is 160°C - 230°C, and the final temperature is 260°C - 300°C; When pre-oxidizing, the fiber tension is 40% - 90% of the breaking stress of the pre-oxidized fiber, preferably 50% - 80%; The bulk density of the fiber obtained after the pre-oxidation is 1.32 g / cm 3 -1.55 g / cm 3 ; Optionally, the carbonization includes low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization; The low-temperature carbonization satisfies one or more of the following conditions: High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 5 ppm; The temperature of the low-temperature carbonization is 300°C - 800°C, and the time is 1.5 minutes - 6 minutes; When low-temperature carbonizing, the fiber tension is 20% - 70% of the breaking stress of the low-temperature carbonized fiber, preferably 40% - 50%; The medium-temperature carbonization satisfies one or more of the following conditions: High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 5 ppm; The temperature of the medium-temperature carbonization is 1000°C - 1400°C, and the time is 1.5 minutes - 6 minutes; During the medium-temperature carbonization, the fiber tension is 20%-70% of the fracture stress of the medium-temperature carbonized fiber, preferably 40%-50%; The high-temperature carbonization satisfies one or more of the following conditions: High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 3 ppm; The high-temperature carbonization temperature is 1400°C - 1600°C, and the time is 1 minute - 4 minutes.

9. The method according to any one of claims 5-7, characterized in that, In step (3), the pre-oxidation satisfies one or more of the following conditions: The pre-oxidation includes 2 - 6 temperature zones; The total treatment time of the pre-oxidation is 40 minutes - 100 minutes; The starting temperature of the pre-oxidation is 160°C - 210°C, and the final temperature is 260°C - 320°C; During the pre-oxidation, the fiber tension is 40%-90% of the fracture stress of the pre-oxidized fiber, preferably 50%-80%; The bulk density obtained from the pre-oxidized fibers is 1.32 g / cm 3 -1.55 g / cm 3 ; Optionally, the carbonization includes low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization. The low-temperature carbonization satisfies one or more of the following conditions: High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 5 ppm; The low-temperature carbonization temperature is 300°C - 800°C, and the time is 1.5 minutes - 6 minutes; During the low-temperature carbonization, the fiber tension is 20%-70% of the fracture stress of the low-temperature carbonized fiber, preferably 40%-50%; The medium-temperature carbonization satisfies one or more of the following conditions: High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 5 ppm; The medium-temperature carbonization temperature is 1000°C - 1400°C, and the time is 1.5 minutes - 6 minutes; During the medium-temperature carbonization, the fiber tension is 20%-70% of the fracture stress of the medium-temperature carbonized fiber, preferably 40%-50%; The high-temperature carbonization satisfies one or more of the following conditions: High-purity nitrogen is used as the protective gas, and the oxygen content in the nitrogen is less than or equal to 3 ppm; The high-temperature carbonization temperature is 1400°C - 1800°C, and the time is 1 minute - 4 minutes.

10. A polyacrylonitrile carbon fiber, characterized in that The polyacrylonitrile carbon fiber is prepared by the method described in any one of claims 1 - 9.

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